1. Field of the Invention
The present invention concerns an optical fiber telecommunication device capable of providing communications between N users.
This device is of a type comprising:
N stations assigned respectively to the N users, each station comprising: PA0 N pairs of optical fibers respectively connected to the N user stations, each pair comprising a transmit optical fiber of which a first end is optically coupled to the output of the laser and a receive optical fiber of which a first end is coupled to the input of the receiver system, and PA0 an interconnection volume filled with a material whose refractive index is similar to that of the material constituting the core of the optical fibers, the second ends of the transmit and receive optical fibers being connected to the surface delimiting this volume. PA0 N-1 optical filters respectively passing only the frequencies F.sub.1 . . . F.sub.p-1, F.sub.p+1 . . . F.sub.N, disposed to receive the receive optical wave transmitted by the receive optical fiber, PA0 N-1 selective electro-optical sensors receiving the respective outputs of the N-1 optical filters, these sensors delivering an electrical signal only if the amplitude of the luminous energy that they receive is modulated at the frequency F.sub.n, PA0 means receiving the electrical signals delivered by the selective sensors and adapted to indicate to the user p the rank n of the filter of frequency F.sub.n the output radiation from which has caused the output of an electrical signal from the selective sensor receiving this output radiation, PA0 an optical conductor one end of which is disposed on the input surface of a photo-electric receiver, and PA0 means for disposing the other end of the optical conductor on the output of the optical filter of frequency F.sub.n. PA0 N stations assigned respectively to the N users, each station comprising: PA0 N pairs of optical fibers respectively connected to the N user stations, each pair comprising a transmit optical fiber of which a first end is optically coupled to the output of the laser and a receive optical fiber of which a first end is coupled to the input of the receiver system, and PA0 an interconnection volume filled with a material whose refractive index is similar to that of the material constituting the core of the optical fibers, the second ends of the transmit and receive optical fibers being connected to the surface delimiting this volume, in which device: PA0 the semiconductor laser is of the tunable emission frequency type and comprises an element adapted to vary the frequency of the transmit optical wave by variation of an electrical current applied to this element, this current being supplied by a tuning circuit whose output is connected to said element, this current adjusting the frequency of the transmit optical wave to a first carrier frequency f.sub.1 when the tuning circuit does not receive any signal, PA0 the device comprises an interconnection central office comprising said interconnecting volume, this central office further comprising: PA0 the receiver system of each station comprises: PA0 a memory connected between the ringing circuit and the modulation circuit to store the ringing signals, and PA0 a control circuit connected to the memory to pass the stored ringing signals into the modulation circuit only within the timing period assigned to the station.
a transmitter circuit adapted to transmit transmit electrical signals, PA1 a semiconductor laser adapted to deliver a transmit optical wave, PA1 a modulation circuit connected between the transmitter circuit and the laser to amplitude modulate the transmit optical wave by the transmit electrical signals, PA1 a photo-electric receiver system adapted to deliver receive electrical signals when it receives a receive optical wave, PA1 a circuit utilizing the receive electrical signals, and PA1 a ringing circuit adapted to form electrical signals for ringing other stations, this ringing circuit being connected to the modulation circuit to provide for amplitude modulation of the transmit optical wave by the ringing signals, PA1 a transmitter circuit adapted to transmit transmit electrical signals, PA1 a semiconductor laser adapted to deliver a transmit optical wave, PA1 a modulation circuit connected between the transmitter circuit and the laser to amplitude modulate the transmit optical wave by the transmit electrical signals, PA1 a photo-electric receiver system adapted to deliver receive electrical signals when it receives a receive optical wave, PA1 a circuit utilizing the receive electrical signals, and PA1 a ringing circuit adapted to form electrical signals for ringing other stations, this ringing circuit being connected to the modulation circuit to provide for amplitude modulation of the transmit optical wave by the ringing signals, PA1 a timing circuit comprising a clock adapted to send periodic timing signals representative of different timing periods assigned respectively to the N stations, PA1 means for transmitting these periods to the respective stations, each station comprising means for amplitude modulating the frequency f.sub.1 of the transmit optical wave by the ringing signals only within the timing period assigned to each station, and PA1 a processor whose input is connected to the interconnection volume in order to receive the ringing signals modulating the frequency f.sub.1, these signals originating from the N stations, the processor designating for each call requested an optical frequency f.sub.p available at the time of the call and selected from a predetermined sequence of frequencies, two consecutive frequencies being separated by a constant frequency interval, the output of the processor being connected to the interconnection volume to transmit the information of the designated frequency f.sub.p, this transmission being effected on a second optical carrier frequency f.sub.2 in the timing periods assigned to the calling and called stations, and PA1 a first photo-electric sensor optically coupled to the first end of the receive optical fiber to receive the signals of frequency f.sub.2 transmitted in the timing period reserved to the station, these signals being transmitted to said tuning circuit for adjusting the frequency of the laser to the designated frequency f.sub.p, PA1 a heterodyne detector system comprising a second photo-electric sensor optically coupled to the first end of the receive optical fiber and a semiconductor local oscillator with a tunable optical emission frequency, the station comprising means for adjusting the frequency of the local oscillator to a frequency f.sub.q near f.sub.p, f.sub.q -f.sub.p being small relative to said constant frequency interval between two consecutive frequencies from the predetermined list, the optical wave emitted by the local oscillator illuminating the receive surface of the second sensor and the output of the heterodyne detector system being connected to the user circuit.
2. Description of the Prior Art
A telephone device of this type is described in the document FR-A-2.472.889.
In this device optical frequencies F.sub.1 . . . F.sub.N and modulation frequencies f.sub.1 . . . f.sub.n are assigned respectively to the N users and the laser of user p delivers a transmit light wave of frequency F.sub.p, this light wave being modulated by the modulation frequency f.sub.n assigned to another user n with whom the user p wishes to communicate.
The receiver system of the station of the user p comprises:
This optical telephone device has the disadvantage of being difficult to employ when the number N of users is high. In this case it is necessary to provide a large number of differing optical frequencies. Also, the receiver system of each user is bulky and difficult to manufacture.
An object of the present invention is to alleviate this disadvantage.